1,977 research outputs found
No Evidence for [O III] Variability in Mrk 142
Using archival data from the 2008 Lick AGN Monitoring Project, Zhang & Feng
(2016) claimed to find evidence for flux variations in the narrow [O III]
emission of the Seyfert 1 galaxy Mrk 142 over a two-month time span. If
correct, this would imply a surprisingly compact size for the narrow-line
region. We show that the claimed [O III] variations are merely the result of
random errors in the overall flux calibration of the spectra. The data do not
provide any support for the hypothesis that the [O III] flux was variable
during the 2008 monitoring period.Comment: Response to Zhang & Feng 2016, MNRAS Letters, 457, L64
(arXiv:1512.07673). Accepted for publication in MNRAS Letters. 5 pages, 2
figure
The polarized EMC effect
Conference details: Quark confinement and the hadron spectrum VII : 7th Conference on Quark Confinement and the Hadron Spectrum, QCHS7, Ponta Delgada, Açores, Portugal, 2-7 September 2006 / José Emílio F. T. Ribeiro (ed.): pp. 248-250We calculate both the spin independent and spin dependent nuclear structure functions in an effective quark theory. The nucleon is described as a composite quark-diquark state, and the nucleus is treated in the mean field approximation. We predict a sizable polarized EMC effect, which could be confirmed in future experiments.W. Bentz, I. C. Cloet, and A. W. Thoma
Analytic approach to nuclear rotational states: The role of spin - A minimal model -
We use a simple field theory model to investigate the role of the nucleon
spin for the magnetic sum rules associated with the low-lying collective
scissors mode in deformed nuclei. Various constraints from rotational symmetry
are elucidated and discussed. We put special emphasis on the coupling of the
spin part of the M1 operator to the low lying collective modes, and investigate
how this coupling changes the sum rules.Comment: 15 pages, 4 figure
Nucleons, Nuclear Matter and Quark Matter: A unified NJL approach
We use an effective quark model to describe both hadronic matter and
deconfined quark matter. By calculating the equations of state and the
corresponding neutron star properties, we show that the internal properties of
the nucleon have important implications for the properties of these systems.Comment: 17 pages, 5 figures, Section 5 extended, references adde
Spin-dependent structure functions in nuclear matter and the polarized EMC effect
An excellent description of both spin-independent and spin-dependent quark
distributions and structure functions has been obtained with a modified
Nambu-Jona-Lasinio model, which is free of unphysical thresholds for nucleon
decay into quarks - hence incorporating an important aspect of confinement. We
utilize this model to investigate nuclear medium modifications to structure
functions and find that we are readily able to reproduce both nuclear matter
saturation and the experimental F^A_2N / F_2N ratio, that is, the EMC effect.
Applying this framework to determine g^A_1p, we find that the ratio g^A_1p /
g_1p differs significantly from 1, with the quenching caused by the nuclear
medium being about twice that of the spin-independent case. This represents an
exciting result, which if confirmed experimentally, will reveal much about the
quark structure of nuclear matter.Comment: 4 pages, 4 figure
Parity-violating DIS and the flavour dependence of the EMC effect
Isospin-dependent nuclear forces play a fundamental role in nuclear
structure. In relativistic models of nuclear structure constructed at the quark
level these isovector nuclear forces affect the u and d quarks differently,
leading to non-trivial flavour dependent modifications of the nuclear parton
distributions. We explore the effect of isospin dependent forces for
parity-violating deep inelastic scattering on nuclear targets and demonstrate
that the cross-sections for nuclei with N /= Z are sensitive to the flavour
dependence of the EMC effect. Indeed, for nuclei like lead and gold we find
that these flavour dependent effects are large.Comment: 4 pages, 2 figure
Dualizability of automatic algebras
We make a start on one of George McNulty's Dozen Easy Problems: "Which finite
automatic algebras are dualizable?" We give some necessary and some sufficient
conditions for dualizability. For example, we prove that a finite automatic
algebra is dualizable if its letters act as an abelian group of permutations on
its states. To illustrate the potential difficulty of the general problem, we
exhibit an infinite ascending chain of finite automatic algebras that are alternately dualizable and
non-dualizable
Implementing PCAC in Nonperturbative Models of Pion Production
Traditional few-body descriptions of pion production use integral equations
to sum the strong interactions nonperturbatively. Although much physics is
thereby included, there has not been a practical way of incorporating the
constraints of chiral symmetry into such approaches. Thus the traditional
few-body descriptions fail to reflect the underlying theory of strong
interactions, QCD, which is largely chirally symmetric. In addition, the lack
of chiral symmetry in the few-body approaches means that their predictions of
pion production are in principle not consistent with the partial conservation
of axial current (PCAC), a fact that has especially large consequences at low
energies. We discuss how the recent introduction of the ``gauging of equations
method'' can be used to include PCAC into traditional few-body descriptions and
thereby solve this long standing problemComment: Contribution to Proceedings, 1st Asia-Pacific Conference on Few-Body
Problems in Physics, Noda/Kashiwa, Japan, 23-28 August 1999, to be published
by Springer-Verlag as "Few-Body Systems Supplement". 7 pages, revtex, epsf, 3
Postscript figure
A reaction-diffusion model for the hydration/setting of cement
We propose a heterogeneous reaction-diffusion model for the hydration and
setting of cement. The model is based on diffusional ion transport and on
cement specific chemical dissolution/precipitation reactions under spatial
heterogeneous solid/liquid conditions. We simulate the spatial and temporal
evolution of precipitated micro structures starting from initial random
configurations of anhydrous cement particles. Though the simulations have been
performed for two dimensional systems, we are able to reproduce qualitatively
basic features of the cement hydration problem. The proposed model is also
applicable to general water/mineral systems.Comment: REVTeX (12 pages), 4 postscript figures, tarred, gzipped, uuencoded
using `uufiles', coming with separate file(s). Figure 1 consists of 6 color
plates; if you have no color printer try to send it to a black&white
postscript-plotte
The NJL-jet model for quark fragmentation functions
A description of fragmentation functions which satisfy the momentum and
isospin sum rules is presented in an effective quark theory. Concentrating on
the pion fragmentation function, we first explain why the elementary (lowest
order) fragmentation process q --> q \pi is completely inadequate to describe
the empirical data, although the "crossed" process \pi --> q \bar{q} describes
the quark distribution functions in the pion reasonably well. Taking into
account cascade-like processes in a generalized jet-model approach, we then
show that the momentum and isospin sum rules can be satisfied naturally,
without the introduction of ad hoc parameters. We present results for the
Nambu--Jona-Lasinio (NJL) model in the invariant mass regularization scheme and
compare them with the empirical parametrizations. We argue that the NJL-jet
model, developed herein, provides a useful framework with which to calculate
the fragmentation functions in an effective chiral quark theory.Comment: 21 pages, 7 figure
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